The 5' cap of eukaryotic and viral messenger RNAs (mRNAs) is a structurally and chemically unique entity located at the 5' terminus of RNAs. It plays a pivotal role in mRNA metabolism, and is required to varying degrees for processing and maturation of the transcript in the nucleus, transport of the message from the nucleus to the cytoplasm, mRNA stability, and efficient translation of message to protein. The 5' cap structure provides resistance to 5'-exonuclease activity, and its absence results in rapid degradation of the mRNA.
Based upon current understanding of the physical and chemical properties of the 5' cap of mRNA, it is believed that its structural or chemical modification leads to the modulation of mRNA expression. Reagents that alter or cleave the 5' cap of mRNA are desirable in the preparation of cDNA libraries where the presence of excessive amounts of some mRNAs make analysis of the less abundant mRNAs difficult and tedious. By altering or cleaving the 5' cap of overabundant mRNAs, those that occur in much lower abundance can be isolated and analyzed.
Selective degradation of a specific mRNA, leading to its inactivation, is of significant utility in the identification and study of the cellular function of that mRNA. Compositions that alter or cleave the 5' cap of mRNAs are desired for their use in distinguishing among the cellular functions of closely related mRNAs.
It is well known that most of the bodily functions in mammals including most disease states, are effected by proteins. Classical therapeutics have generally focused upon interactions with such proteins in efforts to moderate their disease causing or disease potentiating functions.
Recently, attempts have been made to selectively moderate the actual production of such undesired proteins by interactions with molecules that direct their synthesis, intracellular RNA. These interactions involve the binding of complementary "antisense" oligonucleotides or their analogs to the intracellular RNA in a sequence specific fashion by Watson-Crick base pairing interactions. Intracellular hybridization of the two molecules is intended to inhibit either the synthesis and proper metabolism of the selected mRNA or its utilization by the translational machinery in the synthesis of proteins. It is believed that interference with the production of proteins in this manner would yield a therapeutic effect with minimal side effects due to the high level of reaction specificity available through RNA sequence recognition by the antisense molecules [Cancer Res. 48 2659-68 (1988); Pharmaceutical Res. 5 539-49 (1988); Anticancer Drug Design 2 117-128 (1987)].
Several chemical modifications have been introduced into oligonucleotides to increase their therapeutic activity [Nucleic Acid Research 6 3009-24 (1979); Biochemistry 18 5134-43 (1979); Journal of the American Chemical Society 111 2321-22 (1989); Proc. Natl. Acad. Sci. USA 85 7079-7083 (1987); Biochemistry 27 7237-46 (1986), Nucleic Acid Research 14 3487-99 (1986); Nucleic Acid Research 15 4717-36 (1987); Biochemistry 27 3997-4003 (1988); Nucleic Acid Research 15 8643-59 (1987); Acc. Chem. Res. 19. 180-86 (1986).
There is a significant body of published literature that demonstrates the therapeutic utility of antisense oligonucleotides [EMBO Journal 12 1257-1262 (1993); Nature 359 67-70 (1992); J. Clinical Investig. 88 1190-1196 (1991); Science 258 1792-1795 (1992); Proc. Natl. Acad. Sci. USA 90 9901-9905 (1993)]. These references evidence the fact that oligonucleotides can be administered to an animal in vivo, and when so administered an oligonucleotide can be effective in alleviating or diminishing the disease state to which it is directed. It is generally accepted that a clear correlation exists between results obtained by in vitro determination of the ability of specific oligonucleotides to modulate the expression of targeted genes and the activity of the oligonucleotides in vivo.
Published literature also indicates that oligonucleotides have been approved for clinical trials and are being administered to human patients [Antiviral Agents Bulletin 5 161-163 (1992); BioWorld Today, Dec. 20, 1993]. They are known not to have unacceptable toxicity in dosages required for therapeutic use.
Oligonucleotide compositions capable of masking, modifying or cleaving the 5' cap of mRNA are desired as therapeutic agents, and are expected to satisfy the long-felt need for effective therapeutic modalities with either few or no side effects.